Immersion heater and method of making the same



United States Patent Erich L. Gibbs 3001 Martin Luther King Drive,Chicago, 111. 60616 819,293

April 25, 1969 Dec. 8, 1970 inventor Appl. No. Filed Patented IMMERSION-HEATER AND METHOD OF MAKING THE SAME 2,658,984 11/1953 Mohn PrimaryExaminer-Joseph V. Truhe Assistant Examiner-C. L. AlbrittonAttorney-Hill, Sherman, Meroni, Gross & Simpson ABSTRACT: A heatingdevice, particularly for scientific usage as an immersion heater, whichemploys an electrical element for generating radiant energy, in whichthe electrical element is enclosed in a shell, which, for example, maybe of suitable glass having a relatively low coefficient of absorptionwith respect to such radiant energy, such shell having disposed at theexterior surface thereof a material with a relatively high coefficientof absorption of such energy whereby such radiant energy from saidelement will be converted to heat at the exterior surface of said shelland available thereat for substantially direct heating of a fluid inwhich the shell may be immersed.

IMMERSHON HEATER ANDMETMOD OF MAKING 'lll'ilE SAME BACKGROUND OF THEINVENTION The invention is directed to a heating structure, particularlyfor scientific usage and the like in the form of an immersion heaterwhich may be disposed in a fluid to be heated.

In the past, heaters of this general type have employed quartz shells orjackets in which was disposed a nichrome electrical element consistingof a nichrome wire suitably wound and supported on a ceramic core.During operation, a high thermal gradient existed within the heaterstructure which had a deteriorating effect on the ceramic core elementswhereby the latter often cracked during usage and thus necessitatedreplacement in the most expensive portion of the heater unit. Likewise,a heater of this construction, with quartz jacket and ceramic coreelement possesses a relatively large mass which must be brought up tothe desired operating temperatures upon actuation of the heater, andresults in relatively slow cooling following disconnection of theheater, as a result of which fast responsive control by thermostaticdevices was difficult to achieve. Furthermore, in the event ofinsufficient cooling of the unit, prior nichrome elements usually wouldnot burn out until the quartz jacket ruptured with the possibility ofthe occurrence of tire and other damage.

The present invention therefore is directed to a lamp struc ture whicheliminates disadvantages in heaters of the prior type and offersadditional advantages thereover.

BRIEF SUMMARY OF THE INVENTION The present invention contemplates theutilization of a structure in which a relatively low thermal gradientwill exist within the heater structureduring operation, particularlyadjacent the inner face of the outer shell or jacket of the heater,enabling the fabrication thereof from a suitable glass, such asborosilicate glass, at the same time also enabling the use of muchshorter lead-in conductors than heretofore possible, for a similarwattage, with a consequent reduction in the overall length of thestructure and improved efficiency for a given wattage.

Two forms of the invention are illustrated, the first utilizingcommercially procurable tungstenquartz heat lamps, two of which areemployed in the embodiment illustrated, which are removably supportedwithin the shell and thus readily capable of replacement if necessary.In the other embodiment of the invention illustrated, the glass shellforms the enclosing envelope for a tungsten element to provide a unitarystructure.

In both forms of the invention, the glass shell has disposed at theexterior surface thereof a material which is operative to absorb radiantenergy passing through the shell whereby heat developed therefrom isavailable substantially at the exterior of the shell and available forsubstantially direct contact with the fluid to be heated.

The mass of the structure thus is reduced to a minimum whereby thestructure will heat and cool very rapidly, provid ing exceptionallyresponsive heating and cooling cycles so that very close maintenance ofa desired temperature may be achieved.

I have found that a very effective energy absorption material fordisposition at the exterior of the shell is a silver stain comprising amixture of iron oxide with a small amount of silver. Such material maybe effectively disposed on the shell by application in the form of asuspension in a suitable organic medium with the shell being dipped insuch solution and subjected to a heat treatment whereby the stainpenetrates the glass shell, darkening such outer surface to a pointwhere it will efficiently absorb the radiation involved.

In the drawings, wherein like reference characters indicate like orcorresponding parts, and wherein preferred forms of the invention areillustrated, which, as will be apparent therefrom and the followingdescription, may be capable of various immaterial variations andmodifications without departing from the spirit and scope of the novelconcepts of the disclosure:

BRIEF DESCRIPTIONOF THE DRAWINGS FIG. l is an isometric view of oneembodiment of the invention employing removable individual heatingelements;

FIG. 2 is a similar view of another embodiment of the inventionemploying a unitary structure;

FIG. 3 is a longitudinal section through the tube illustrated in FIG. 1and a portion of the mounting structure therefor;

FIG. 4 is a sectional view taken approximately on the line lV-lV of FIG.3;

FIG. 5 is an end view of a fitting for supporting the inner ends of theindividual heating tubes of the construction illustrated in FIG. I;

FIG. 6 is a side elevational view of the fitting illustrated in FIG. 5;

FIG, 7 is a top plan view of one of two like fittings employed tosupport the outer ends of the respective heating elements ofconstruction illustrated in FIG. 1;

MG. 8 is a side elevational view of the fitting illustrated in 7 FIG. 7;

FIG. 9 is a longitudinal sectional view, similar to FIG. 3, of theembodiment illustrated in FIG. 2; and

FIG. it) is a sectional view taken approximately on .the'line X-X ofFIG. 9.

DETAILED DESCRIPTION Two embodiments are illustrated in the drawings,one of which, illustrated in FIGS. 1 and 3, utilizes commerciallyprocurable tungsten-quartz heat lamps of a type commercially procurable,as for example, tungsten-quartz infrared heat lamps manufactured byGeneral Electrical Company and identified as GE8OOT3. The otherembodiment illustrated in FIGS. 2 and 9, employs a unitary constructionin which the heating element is constructed 'as a unitary part of theentire structure, and in which case the interior of the device issuitably evacuated or provided with a low-pressure atmosphere inaccordance with standard practice for heating elements of this generaltype.

Both of the constructions illustrated utilize a glass shell, at theouter surface of which is disposed the desired radiation absorbingmaterial, for example, in the form of a stain which penetrates the glasswall of the shell at the exterior surface thereof.

THE CONSTRUCTION WITI-I REPLACEABLE HEATING ELEMENTS Referring to thedrawings and more particularly to FIGS. 1, 3 and 4-8, the referencenumeral 1 designates an elongated hollow tubular shell constructed of asuitable glass, for example a borosilicate glass, having one end thereofclosed as indicated at 2 and the opposite end thereof open as indicatedat 3. Such open end of the shell is provided with a peripheral flange i,which as illustrated in FIG. 3, may be provided with one ormore flats 5forming means for effecting proper registration between the end of theshell and a cooperable end assembly indicated generally by the numeral6. The shell 1 is also provided with a conical or tapered wall portion7, illustrated in the present embodiment as being disposed adjacent tobut spaced from the open end 3 of the shell, with the outer surface ofthe portion 7 being suitably formed, as for example by grinding, toprovide a sealing surface adapted to cooperate with a complementallyshaped portion 8 forming a part of a vessel 9 or other structure inwhich the heater is to be operatively supported.

Disposed in the shell 1 are a pair of heat lamps, each indicatedgenerally by the numeral 11, each of which comprises an elongatedtubular-bulb 12 of quartz, the ends of which ,are suitably sealed andcapped by terminal members 13, which in the commercial construction areconstructed of sheet metal formed about the sealed bulb end andconductively connected to opposite ends of a tungsten wire element 14,the intermediate portion of which is formed in the shape of a smalldiameter helix 15. The latter, as illustrated, may be formed in aplurality of sections with suitable spacer elements 16 being disposedbetween the respective sections operable to support the element 14 infixed spaced relation with respect to the tubular side walls of the bulb12.

The inner ends of the respective lamps 1 1 are supported in a fitting17, preferably of a material having a good thermal conductivity, as forexample aluminum, the fitting 17 being generally cylindrical and havinga pair of spaced parallel slots 18 therein which intersect one end ofthe fitting and are of a size to snugly receive the terminal members 13at the inner ends of the respective heat lamps. Such heat lamps in theircommercial form are provided with respective lead-in conductors 19, ofrelatively short length which are secured to the respective terminalmembers 13 and thus to the adjacent end of the associated heatingelement 14, which conductors, as illustrated in FIG. 3, are adapted tobe inserted through axially extending bores 21 in the fitting 17, suchbores being located in the bottom wall of the respective slots 18 andpositioned to be aligned with the lead-in conductors 19 whereby thelatter may be extended substantially straight through the fitting 17 sothat upon suitable connection of the two conductors an efficientelectrical connection may be made between the adjacent terminals 13.Where the fitting 17 is fabricated of metal, such as aluminum, and soproportioned that the terminal members 13 are snugly received in theslots 18, the fitting 17 likewise may function as an electricalconnector between the two terminal members 13.

The terminal members 13 at the opposite ends of the respective heatlamps II are supported in a similar manner from a cooperable structure,constructed in the form of an assembly 22 comprising a pair of members23, of like construction, cooperable with an'intermediate insulatingstrip 24 to form a generally cylindrical assembly with each member 23having a slot 18' thereiri, corresponding to the slots 18 of the fitting17, into which are received the respective adjacent terminal members 13of the heat lamps 11. Each of the members 23 is provided with a bore 25therein, corresponding to the bores 21, suitably placed to receive thelead-in conductor of the adjacent terminal member 13, which, afterpassing through an insulating disk 26, are extended for connection,exteriorly of the shell 1, with a power line. In the embodimentillustrated, the member 23 and insulating strip 24 are normally retainedin aligned assembled relation by a short section of glass tube 27disposed in aligned bores 28 in the member 23 and a similar bore in thestrip 24.

The end assembly 6, in the embodiment of the invention illustrated,comprises a pair of cooperable annular-shaped members 31 and 32.,constructed for example of aluminum or other metal, which are assembledwith a disk or block of suitable insulating material 33 interposedtherebetween, which in the embodiment illustrated is provided with acentral portion 34 of increased thickness which carries a pair of pinterminals 35, the lead-in conductors 19' being extended to the member 33and secured in conductive relation to the terminals 35. The member 32,in the embodiment illustrated is provided with a tubular portion 36,cooperable with the terminals 35 to form an electrical connector bymeans of which the heating ele ments may be operatively connected to apower source. The member 32 may be suitably secured to the member 31 bya plurality of screws 37 or the like. As previously mentioned, theflange 4 at the open end of the shell 1 may be provided with a flat 5,with the member 31 being provided with a counterbore 38 therein of asize to receive the flange 41, such counterbore preferably having ashape complemental to the flange 4. including the flat whereby the endassembly 6 is rotationally fixed with respect to the shell 1, thusmaintaining the connector structure in proper alignment with respect tothe conductor leads 19' from the respective lamps.

Disposed between the insulating disk 33 and the insulating disk 26 is acompression spring 39 operated to urge the entire internal assembly intofixed relation with respect to the shell structure, and in particular toprovide a firm seating of comnlemental portions of the fitting 17 andthe fittings 23 in engagement with the inner surface of the shell 1 toprovide good heat conduction from such fittings to the walls of theshell, from which the heat may be suitably dissipated.

As illustrated in FIG. 1, the major portion of the shell 1, extendingfrom the tapered portion 7 is provided with a suitable material 40 whichwill absorb the radiation emitted by the lamps 11.

The material 40 may comprise any suitable components preferably beingapplicable to the tube in the form of a stain which will penetrate theglass a slight distance and thus forms a permanent part of the shellwhich cannot be inadvertently removed or damaged other than whenassociated with destruction of the shell itself.

I have found that a silver stain comprising mainly iron oxide, to whicha small amount of silver is added is suitably dispersed in an organicvehicle, as for example, isopropyl alcohol. A suitable stain may also becommercially procured, as for example that known as amber stain 29-346marketed by the Drakenfield Company, which it is believed is a materialcorresponding to the iron oxide-silver material above described.

I have found that highly superior results can be achieved in theapplication of material if the latter takes places in accordance with aspecific and accurately controlled process, whereby the finishedmaterial is in the form of a stain which penetrates the glass shell atthe outer surface thereof, penetrating the latter for a very shortdistance, as compared with the thickness of the wall, as for example,several thousandths of an inch. In producing such stained layer, theshell preferably is dipped in a solution of the material and thensubjected to a heat treatment at a temperature of approximately 1000 F.The exact temperature will depend upon the variables involved, thecomposition of the glass, proportions of the staining materials, and thevehicle therefor, and may be readily determined by test. I have foundthat the staining materials apparently are sensitive to overheating,stain tending to fade or wash out when the temperature becomes too high.Consequently, test should be run to determine the point at whichdeterioration of the stain takes place and then employ a temperaturewhich is adequately therebelow. Depending on such factors, a suitabletemperature will fall within approximately 950 F. to 1 F. Such dippingoperation is repeated until the exterior of the glass darkens to such anextent that it appears black in reflected light and a deep thin red bytransmitted light, usually with three or four clippings. The thinstained layer so formed absorbs visible light and transmits mainly lightin the red and infrared ranges. The heat lamps of the type describedradiate over 85 percent of their emitted energy and have a long lifeexpectancy of 5000 hours or more.

It will be appreciated that as most of the energy is radiant, and as airand clear glass absorb very little of the radiated energy, most of suchenergy travels from the heated tungsten element to the stained layer ofthe shell with relatively little absorption taking place and thus littleheat generation. Tests indicate that the temperature of the shellinterior, in a construction as illustrated in H6. 1, will normally fallwithin C. to 250 C. However, at the stained layer, most of the radiantenergy is absorbed and given off as heat. Consequently, where the shell1 is immersed directly into the liquid to be heated, the heat isdeveloped substantially directly at the liquid with no conduction travelthrough the heating structure.

It will also be noted that heat is effectively conducted away from theend seals and terminal members 13 of the heat lamps by the respectivefittings l7 and 23 which are in conductive engagement with the innersurface of the shell 1 and are thus operative to conduct heat at suchterminals to the shell, from which it may be suitably dissipated. Thefittings 17 and 23 preferably are suitably coated, as for example goldplated, to provide a lasting finish thereon which will be highlyefficient in reflecting the radiated energy, thereby tending to reducethe formation of heat in such fittings. This is of importance ascommercially procurable lamps, such as the one referred to, are soconstructed that the end seals of the respective tubes may fail attemperatures above 650 F. thereby permitting entrance of air and burningout of the filament. As a result, this construction provides anautomatic safety cutoff in the event the temperature of the shellbecomes excessive, for example, as the result of improper fluidcirculation around the tube. Where two heat bulbs are employed asillustrated, obviously upon failure of one bulb, the other will remainintact and as the internal structure of the device is readily removablefrom the shell, replacement of a burned out element is no problem.

It will be appreciated that this embodiment of the invention provides anumber of distinct advantages over prior types of structures, amongwhich are the fact that the tungsten-quartz lamps are self-supportingand generally cheaper than nichrome elements, which of necessity arewound on expensive thermal shock resisting ceramic cores, etc. and atthe same time the nonabsorbed visible emission from nichrome typeheaters is greater than that of tungsten type heaters such as hereinvolved, as a result of which nichrome heaters would be less efficientfor clear colorless liquids and in same cases might even causeundesirable chemical reactions.

It will also be noted from the above description that the low thermalgradient within the present construction is nonlinear, in general havingtwo peaks, one adjacent the filament and one at the stained layer, withcomparatively much lower temperatures in between such peaks.Consequently, much shorter lead-in arrangement is possible with thepresent invention than with nichrome types of similar wattage, with acorresponding decrease in the overall length of the structure.

Likewise, as previously mentioned because of the absence of relativelylarge masses which must be heated and cooled, the invention enables theproduction of a heater which both heats and cools very rapidly enablingthe use of relatively short cycles and the maintenance of desiredtemperatures within very narrow limits.

While I prefer to employ an energy absorbing material in the form of astain'whichpenetrates the glass, other materials in other forms may beemployed, provided that they have reasonably suitable characteristicswhich should include suitable absorption characteristics, no undesirablereflective characteristics which might tend to reflect energy back'intothe shell, and which possess adequate durability with respect toretention or. the shell surface, etc.

UNITARY HEAT CONSTRUCTION FIGS. 2, 9 and illustrate an embodiment of theinvention in which the shell carrying the energy absorbing material alsofunctions as the envelope for the heating element, and as the shell maybe formed from a suitable glass, the use of quartz structures iscompletely eliminated.

Referring to FIGS. 2, 9 and it), the shell 1' is provided with an openend 3, having an outwardly extending flange 4 and a conical shapedportion 7, of similar construction to the corresponding portions of theshell 1 of the construction of FIG. 3, the portion 7 preferably beingground on its external face to provide an efficient mating with thecomplemental bore 8 in the vessel 9. Likewise, the flange 4 may beprovided with one or more flats for cooperation with respective elementsof the assembly 6.

In this embodiment, the heating element 14, of tungsten wire or thelike, and which may be wound in a relatively tight helical or helicalsections 15, is arranged in a substantially U- shaped configuration withthe respective ends thereof being secured to a glass stem 43 carried bythe glass end wall 42 forming the closure for the adjacent end of theshell. The latter is provided with two spaced, parailel tubular portions43, of relatively small diameter as compared with the diameter of thecorresponding portion of the shell 1, and of a size to suitably enclosethe corresponding portions of the heating element 14, with outer ends ofthe tubes 43 being connected by an intermediate portion 44, and theopposite ends of the tubes secured in sealed relation to the conicalportion 7, thereby completely enclosing the heating element. The stem lland wall 42 may be provided with an exhaust passage or bore 45 throughwhich the shell may be suitably evacuated or at least partially filledwith a suitable gas, following which the outer end portion may be sealedas indicated at 46. The respective sections 15 of the heating element14, as in the construction of FIG. 3, may be suitably supported in theshell by a plurality of spacer elements 16.

The end assembly 6 may be substantially identical construction with thatof FIG. 3, the connector pins 35 however preferably being provided withrelatively rigid, inwardly extending portions 35' to which the free endsof the electrical element 14 are conductively connected.

As will be apparent from reference to FIG. 2, the U-shaped portion ofthe shell 1 is stained as indicated at 40' to provide the desiredabsorption of radiant energy passing through the shell.

The operation of the embodiment of FIG. 2 is substantially identicalwith that of FIG. 1 with the exception that the heating element andshell form a single unitary structure. The

general operation likewise will be the same,.radiant energy from theelement 14 passingthrough the glass shell and being substantiallycompletely absorbed in the stained layerof the shell. While theembodiment of FIG. 2 does not possess the advantage of replaceableelements, it does have the further advantage that the quartz bodies areeliminated with a reduction in the thermal heat developed within theshell and thus providing a greater percentage of the output in the formof radiated energy.

Obviously, where deemed necessary or desirable, the portions 43 and 44may have a configuration other then U- shaped, and in some cases, it maybe desirable to employ a tubular shell similar to that illustrated inFIG. I.

I claim:

1. An immersion type heating device, particularly for scientific usage,comprising a shell of glass constructed for direct immersion in a fluidto be heated and having high transmission characteristics with respectto radiant energy, an electrical element disposed in said shell,operative to transmit radiant energy through the walls of the latter,and a material having high absorption characteristics with respect tosuch radiant energy, disposed at the exterior surface of said shelloperative to absorb radiant energy passing therethrough whereby radiantenergy transmitted from said element, upon striking said material, isthereby converted at said exterior surface into heat utilizable forheating, by conduction, of such a fluid thus providing directdissipation of heat from said material and supporting shell to such afluid.

2. A heating device according to claim 1, wherein said shell isconstructed of a borosilicate glass and said high absorption materialcomprises an applied mixture of iron oxide and silver.

3. A heating device according-to claim 2, wherein said high absorptionmaterial is disposed on said shell in the form of a stain whichpenetrates the shell'material for a distance which is small, as comparedwith the thickness of said shell.

4. A heating device according to claim 3, wherein said stain penetratessaid shell material to a depth of at least several thousandths of aninch.

5. A heating device according to'claim 1, wherein said electricalelement comprises at least one tungsten-quartz heat lamp, and means forsupporting said electrical element in operative relation with respect tosaid shell.

6. A heating device according to claim 1, wherein said electricalelement comprises a tungsten element disposed directly in said shell,with the atmosphere of said shell interior being at a reduced pressurecompared with that exteriorly of the shell to form a unitary heat lamp.

7. A heating device according to claim 6, wherein said shell has atubular portion of, U-shaped configuration which contains said tungstenelement.

8. A heating device according to claim 7, wherein said material isdisposed on the U-shaped portion of said shell.

9. A conduction-type heating device comprising means constructed togenerate radiant energy, an enclosing shell for said means constructedof a material having a relatively low absorption factor withrespect'to'radiant energy generated by said means, and means penetratinginto the shell wall at the exterior surface thereof having a relativelyhigh absorption factor with respect to such radiant energy, whereby theusable supply of heat, as a result of such absorption, is generatedprimarily at the exterior surface of said shell and transmitted byconduction to a liquid in contact therewith.

10. The method of forming an immersion-type heating device utilizingradiant energy, comprising the steps of fabricating a shell of amaterial that has a relatively low absorption characteristic withrespect to the radiant energy to be employed, applying a materialcapable, upon the application of heat thereto, of forming alayer at theouter surface of said shell which is highly absorbent to the radiantenergy involved, upon said shell, subjecting the coated shell to heat toeffect a stainlike penetration of the shell at the outer surfacethereof, thereafter applying a second coating of said material to theouter surface of said shell and subjecting the same to a like heattreatment, repeating such coating and heating steps until the resultantlayer of material penetrated into the shell wall at the exterior thereofis sufficient to provide absorption of at least the major part of suchradiant energy normally striking said layer, and thereafter assemblingin said shell means for generating such radiant energy.

111. The method according to claim 10, wherein said materia] primarilycomprises iron oxide, to which a relatively small amount of silverpowder is added, such mixture being suspended in an organic vehicle,said material being applied to I said shell by dipping the latter intosuch material-containing vehicle.

12. The method according to claim 11, wherein said heating steps areeffected at a temperature of approximately 1000 F.

13. The method according to claim 11, wherein said organic vehiclecomprises isopropyl alcohol.

14. In a heating device,'particularly for scientific usage, thecombination of a shell of glass constructed for immersion in a fluid tobe heated, said shell comprising an elongated tube closed at one end, anelectrical element disposed in said shell, operative to transmit radiantenergy through the walls of the latter, said element comprising a pairof tungsten-quartz heat lamps of elongated cylindrical configurationdisposed in coextensive parallel relation, said lamps having connectingterminals at each of their respective ends, lamp-supporting meanscomprising a fitting at the inner end of said shell engaged with theinner end terminals of the respective lamps at the inner end of saidshell, such inner end terminals being conductively connected, and a pairof spaced cooperable fittings at the opposite ends of said lamps, eachadapted to engage a corresponding adjacent lamp terminal, whereby thelatter are supported in spaced insulated relation, and supply leadsextending from said terminals for connection to an electrical powersource, said fittings being constructed of a heat-conductive materialand disposed in heat conductive relation with respect to said shell fordissipating heat at said terminals to said shell, and a materialoperative to absorb radiant energy passing through said shell, disposedat the exterior surface of the latter, whereby radiant energy from saidelement utilizabie for heating of such a fluid is available therefor atsaid material.

15. A heating device according to claim 14, wherein said fittings aremetallic and are coated with a plating of gold for the eflicientreflection of radiant energy away from the end terminals of said lamps,as well as heat conduction from said terminals to said shell.

16. A heating device according to claim M, comprising in furthercombination, a flange formed on the open end of said shell, a closurestructure secured to the flange end of said shell and a compressionspring disposed between said closure structure and the adjacent endfittings operative to apply compression forces thereto for firmlymaintaining the latter and associated lamp elements in operativeposition within said shell.

